They are soild as a rock!! 3/4"
I got something called Seaboard, same as Starboard in every way, but price!
I live in Ma and got in Boston. Maybe you can call them to see were there is a suplier near you?
Here is info on Seaboard
http://www.modernplastics.com/june05/wdseaboard.html
1-800-243-9696
Price for different sheets
https://secure15.nexternal.com/share...unt2=178687691